STEROL CARRIER PROTEIN-2 MEDIATED CHOLESTEROL ESTERIFICATION IN TRANSFECTED L-CELL FIBROBLASTS

The relative function of the 15 and 13.2 kDa forms of SCP-2 in cholest erol trafficking and metabolism was assessed using L-cell fibroblasts permanently transfected with the cDNA encoding for either the mouse 15 kDa or 13.2 kDa SCP-2. Expression of the 15 kDa, but not the 13.2 kDa SCP-2 increased [H-3]cholesteryl ester formation from medium derived cholesterol by 30% compared to control cells. In both SCP-2 expressing cell lines, sphingomyelinase treatment increased the initial rate of [H-3]cholesteryl ester formation from plasma membrane derived choleste rol more than 11-fold and elevated [H-3]cholesteryl ester levels 1.5-f old compared to control cells. Expression of both proteins resulted in nearly a 1.5-fold increase in [H-3]oleic acid esterification into cho lesteryl esters, although [H-3]oleic acid esterification into triacylg lycerols was also increased in the 13.2 kDa SCP-2 expressing cells rel ative to control. In both transfected cell lines, the cholesteryl este r mass was increased nearly 2-fold compared to control cells, consiste nt with increased cholesteryl ester synthesis. Similarly, triacylglyce rol levels were increased 1.3-fold in the 13.2 kDa SCP-2 expressing ce lls which is consistent with the increased [H-3]oleic acid esterificat ion into triacylglycerol. In the 15 kDa SCP-2 expressing cells, triacy lglycerol levels were decreased 60%, but free cholesterol levels were increased 1.2-fold relative to control cells. Thus, only the 15 kDa ex pression product, containing the putative targeting sequence, specific ally enhanced cholesteryl ester formation from either plasma membrane or medium-derived cholesterol. In contrast, the 13.2 kDa expression pr oduct, lacking the putative targeting sequence, stimulated an increase in [H-3]oleic acid esterification into both cholesterol and triacylgl ycerol pools, suggesting a non-specific stimulation of fatty acid este rification. (C) 1997 Elsevier Science B.V.